diff --git a/doc/requirements.txt b/doc/requirements.txt
index ae2d2e0e5..26973d407 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,5 +1,5 @@
 # sphinx version requirement for readthedocs.
-sphinx==8.2.3
+sphinx==9.1.0
 sphinx-rtd-theme==3.1.0
 sphinxcontrib-spelling==8.0.0
 certifi>=2023.7.22 # not directly required, pinned by Snyk to avoid a vulnerability